Engineering topics

Gioia, Isabella M.

Publications and source records attributed to Gioia, Isabella M..

At least 19 records

NASA NTRS1999

The Second Most Distant Cluster of Galaxies in the Extended Medium Sensitivity Survey

We report on our ASCA, Keck, and ROSAT observations of MS 1137.5+6625, the second most distant cluster of galaxies in the Einstein Extended Medium Sensitivity Survey (EMSS), at redshift 0.78. We now have a full set of X-ray temperatures, optical velocity dispersions, and X-ray images for a complete, high-redshift sample of clusters of galaxies drawn from the EMSS. Our ASCA observations of MS 1137.5 +6625 yield a temperature of 5.7 (+2.1)(-1.1) keV and a metallicity of 0.43 (+40)(-3.7) solar, with 90% confidence limits. Keck II spectroscopy of 22 cluster members reveals a velocity dispersion of 884 (+185)(-124) km 24/s. This cluster is the most distant in the sample with a detected iron line. We also derive a mean abundance at z = 0.8 by simultaneously fitting X-ray data for the two z = 0.8 clusters, and obtain an abundance of Z(sub Fe) = 0.33 (+.26)(-.23). Our ROSAT observations show that MS 1137.5+6625 is regular and highly centrally concentrated. Fitting of a Beta model to the X-ray surface brightness yields a core radius of only 71/h kpc (q(sub o) = 0.1) with Beta = 0.70(+.45)(-.15) The gas mass interior to 0.5/h Mpc is thus 1.2 (+0.2)(-0.3) X 10(exp 13) h(exp - 5/2) Solar Mass (q(sub o) = 0.1). If the cluster's gas is nearly isothermal and in hydrostatic equilibrium with the cluster potential, the total mass of the cluster within this same region is 2.1(+1.5)(-0.8) X 10exp 14)/h Solar Mass, giving a gas fraction of 0.06 +/-0.04 h (exp -3/2). This cluster is the highest redshift EMSS cluster showing evidence for a possible cooling flow (about 20-400 Solar Mass/yr). The velocity dispersion, temperature, gas fraction, and iron abundance of MS 1137.5+6625 are all statistically the same as those properties in lower red- shift clusters of similar luminosity. With this cluster's temperature now in hand, we derive a high-redshift temperature function for EMSS clusters at 0.5 < z < 0.9 and compare it with temperature functions at lower redshifts, showing that the evolution of the temperature function is relatively modest. Supplementing our high-redshift sample with other data from the literature, we demonstrate that neither the cluster luminosity-temperature relation, nor cluster metallicities, nor the cluster gas evolved with redshift. The very modest degree of evolution in the luminosity-temperature relation inferred from these data is inconsistent with the absence of evolution in the X-ray luminosity functions derived from ROSAT cluster surveys if a critical density structure formation model is assumed.

Donahue, Megan↗

NASA NTRS1997

X-Ray Gas Temperatures in the Arc Clusters MS0440+204 and MS0302+1658

The cluster of galaxies MS0440+02, originally discovered through its X-ray emission, was part of an optical observational program to search for arcs and arclets in a complete sample of X-ray luminous, medium-distant clusters of galaxies. Mauna Kea CCD images of MS0440+02 showed a remarkable optical morphology. The core of the cluster contains 6 bright galaxies and numerous fainter ones embedded in a low surface brightness halo. Besides, MS0440+02 is the most spectacular example that we have found of an arc system in a compact condensed cluster, with arcs symmetrically distributed to draw almost perfect circles around the cluster center. Giant arcs are magnified images of distant galaxies, gravitationally distorted by massive foreground clusters. It is of great importance to compare the results of the lensing studies with those derived from X-ray observations, as the two are independent methods of studying the mass distribution. Thus MS0440+02 was the ideal target to obtain temperature measurement with ASCA and good spatial resolution X-ray observations with ROSAT. The X-ray data have been used in conjunction with Hubble Space Telescope observations to put more stringent constrains on the mass estimates. Most of the different wavelength datasets have been reduced and analyzed. Mass determinations have been separately obtained from galaxy virial motions and X-ray profile fitting using the cluster gas temperature as measured by the ASCA satellite. Assuming that the hot gas is in hydrostatic equilibrium and in a spherical potential, we find from the X-ray data a mass distribution profile that is well described by a Beta model. From the multiple images formed by gravitational lensing (HST data) using the modelling of the gravitational lensed arcs, we have derived Beta model. To reconcile the mass estimates we have explored the possibility of having a supercluster surrounding the MOS0440 cluster, that is a model with two isothermal spheres, one embedded inside the other. These results have been published or are in press.

Gioia, Isabella M.↗

NASA NTRS1994

ROSAT observations of four unidentified EMSS sources

We present an analysis of four unidentified Einstein Observatory Extended Medium Sensitivity Survey sources detected in two pointed ROSAT/Position Sensitive Proportional Counter (PSPC) observations. One source (MS0420.0-3838) is resolved in two sources denoted with N (North) and S (South) in the ROSAT image. Only for one source (MS0420.6-3839) we have enough counts to allow a spectral analysis. For the other sources we have limited ourselves to the calculation of the x-ray hardness ratio and then, assuming a galactic value for the hydrogen column density, we have derived an energy index alpha (sub epsilon). We find a wide range of alpha(sub epsilon) (1 equal to or less than alpha(sub epsilon) equal to or less than 3). Thanks to a significantly improved x-ray positional accuracy, generally only one or two objects down to approx. 22 mag are present in the error circle. We have spectroscopically identified three sources with AGN: two are radio-quiet Quasi-Stellar Object (QSO) at z = 0.831 and z = 0.482, the third one is a Narrow Emission Line Galaxy at z = 0.572. For the remaining sources no optical spectroscopy is available; however, the values of alpha(sub ox) and alpha(sub ro) show that also these sources are probably AGN.

Ciliegi, Paolo↗

NASA NTRS1992

The properties of X-ray selected active galactic nuclei. II - A deeper look at the cosmological evolution

A detailed study of the cosmological properties of X-ray selected AGN is presented. The data are analyzed within the framework of a pure luminosity evolution (PLE) model and the two most population evolutionary forms. Evidence is found for luminosity-dependent luminosity evolution if the evolution function has the exponential form. The simpler PLE model is more acceptable if the data are fitted with a power-law evolution function. Similar results are obtained in the optical domain from an analysis of a sample of optically selected QSOs with z less than 2.2 and B less than 20.

Della Ceca, Roberto↗

NASA NTRS1990

MS 1603.6 + 2600, an unusual X-ray selected binary system at high Galactic latitude

The discovery of an eclipsing binary system at Galactic latitude 47 deg, found as a serendipitous X-ray source in the Einstein Extended Medium Sensitivity Survey, is described. The object has X-ray flux 1.1 x 10 to the -12th ergs/sq cm s (0.3-3.5 keV) and mean magnitude R = 19.4. An orbital period of 111 minutes is found. The problem discussed is whether the system has a white dwarf or neutron star primary, in the end preferring the neutron star primary model. If the system has either optical or X-ray luminosities typical of low mass X-ray binaries (LMXB), it must be at a very large distance (30-80 kpc). Blueshifted He I absorption is seen, indicating cool outflowing material, similar to that seen in the LMXB AC 211 in the globular cluster M15.

Morris, Simon L.↗

NASA NTRS1990

MS 0129.2 - 2237 - Interacting galaxies at z = 0.11

The X-ray source MS 0129.2 - 2237 is positionally coincident with an interacting system of galaxies. This paper presents the results of a spectroscopic and photometric investigation of the system, which show that a Seyfert 1.5, a Seyfert 2 nucleus or H II region, or a starburst galaxy, a normal galaxy plus possibly another galaxy where star-forming activity is taking place are strongly interacting. The redshift of the system is z = 0.11. The maximum projected diameter of the envelope common to the four spectroscopically distinct objects is about 98 kpc (H0 = 50 km/s M/pc and q0 = 0.5). The isolated environment in which the system lies suggests that these results present evidence of the final stage of the life of a compact group of galaxies where members are merging into an elliptical galaxy.

Maccagni, Dario↗

NASA NTRS1989

BL Lacs from the EMSS: Number-counts and implications for the luminosity function

BL Lac objects, extracted from the Einstein Extended Medium Sensitivity Survey (EMSS), are examined. X-ray selection proved to be a powerful tool to find new BL Lacs, and allows the creation of complete, well defined and sizable samples. X-ray selected BL Lac objects (XBL) have in general more starlight in the optical spectra than radio selected BL Lacs. Redshifts for a significant fraction of objects in samples of XBL can be determined. It is thus possible to study the cosmological properties of BL Lac objects. Different models of luminosity functions of BL Lacs, including relativistic beaming, are considered and integrated over luminosity and redshift. The results are compared with the observed number-counts. The observed redshift distribution and the models' predictions are analyzed.

Wolter, Anna↗

NASA NTRS1989

A cooling flow in a high-redshift, X-ray-selected cluster of galaxies

The X-ray cluster of galaxies IE 0839.9 + 2938 was serendipitously discovered with the Einstein Observatory. CCD imaging at R and V wavelengths show that the color of the dominant elliptical galaxy of this cluster is significantly bluer than the colors of the next brightest cluster galaxies. Strong emission lines, typical of cD galaxies with cooling flows, are present in the spectrum of the dominant galaxy, from which a redshift of 0.193 is derived. The emitting line region is spatially resolved with an extension of about 13 kpc. All the collected data suggest that this cluster is one of the most distant cooling flow clusters known to date.

Nesci, Roberto↗

NASA NTRS1989

X-ray-selected candidates for the RS CVn and W UMa classes of binary stars

X-ray luminosity, spectral type, radial-velocity variation, rotationally broadened line profile, and Ca II H and K line emission data are used to identify 12 new candidates for the RS CVn class and seven new candidates for the W UMa class from spectroscopic binaries which are contained in the Einstein Extended Medium Sensitivity Survey. Under the assumption that the candidates are genuine members of each class, local space density estimates of 4.47 + or - 1.19 x 10 to the -4th/cu pc for RS CVn binaries and 8.47 + or - 3.00 x 10 to the -5th/cu pc for W UMa binaries are found. Although the density estimate for the W UMa binaries is shown to be consistent with previous estimates obtained from optically selected samples, the estimate for the RS CVn binaries is more than an order of magnitude greater than previously determined space densities.

Fleming, Thomas A.↗

NASA NTRS1989

The relation between X-ray emission and rotation in late-type stars from the perspective of X-ray selection

An X-ray-selected sample of 128 late-type (F-M) stars analyzed. These stars were identified as optical counterparts to serendipitous X-ray detections made by the Einstein Observatory Extended Medium Sensitivity Survey. Once identified as X-ray sources, the sample was followed up by an extensive program of optical observations, including high-resolution and low-resolution spectroscopy and photometry. Spectral types, luminosity classes, distances, X-ray luminosities, projected rotation rates (v sin i), radial velocities, and binary status have been determined for the sample.

Fleming, Thomas A.↗

NASA NTRS1988

M dwarfs from the Einstein extended medium sensitivity survey

A complete sample of X-ray selected M dwarfs are presented which were serendipitously detected in the extended Einstein Observatory Medium Sensitivity Survey (MSS). The MSS detected only early M dwarfs (type MO through M5), 84 percent of which were emission stars (i.e., type Me V). It was calculated that the X-ray luminosity function for early M dwarfs with a log Lx greater than 27.6 and, by comparison to optical luminosity functions, find that about 25 percent of all early M dwarfs emit X-rays at a level greater than log Lx = 27.6. This result is compared to luminosity function estimates from optically selected samples and discussed in light of the sample's kinematic and mean age. Also presented is H alpha and Ca II K line fluxes for each member of the sample and it is shown that the surface H alpha and Ca II K luminosities do indeed correlate with Lx. The significance of this effect to theories of chromospheric and coronal heating is explained.

Fleming, Thomas A.↗

NASA NTRS1988

The X-ray spectra of the extragalactic sources in the Einstein extended medium sensitivity survey

The X-ray energy distribution of a large sample of faint extragalactic X-ray sources is studied. Two independent methods are used to determine that the average spectral index for the sources is about 0.95. The intrinsic dispersion of the spectral index distribution is about 0.36. The sources are characterized by a range of power law slopes in the soft X-ray band with a mean of 1.03 + 0.05 or - 0.06 and an intrinsic dispersion of about 0.36. The present analysis extends knowledge of the AGN spectral properties to sources which are about three times more distant and more than 10 times fainter than those previously studied. There is no evidence in the data for any change in the mean spectral index of either extragalactic sources as a whole or AGN in particular, as a function of the X-ray flux in the flux range 10 to the -11th to 10 to the -13th ergs/sq cm/s.

Maccacaro, Tommaso↗

NASA NTRS1987

1E 1751 + 7046 - A new FK comae candidate

1E 1751 + 7046 is a star that was serendipitously detected by the Einstein Observatory Medium Sensitivity Survey. X-ray, optical, and radio observations of this star show it to have characteristics similar to the RS CVn binaries. However, repeated high-resolution spectroscopic observations fail to detect any significant radial-velocity variations. The possibility of the star being pre-main-sequence is dismissed because of its location and lack of photospheric Li I. This makes 1E 1751 + 7046 an attractive candidate for the recently proposed class of FK Comae stars. Although there is disagreement over the evolutionary status of these evolved stars, they are nonetheless interesting as exhibitors of extreme chromospheric and coronal activity.

Fleming, Thomas A.↗

NASA NTRS1987

X-ray-selected AGNs near bright galaxies

Among the numerous low-redshift low-luminosity X-ray sources discovered with the Einstein Observatory, ten AGNs were identified that are projected within three optical diameters of bright (V less than 18) foreground galaxies. These AGNs near galaxies have significantly higher redshifts than the sample as a whole. This discovery is interpreted in terms of gravitational 'microlensing' in which stars in the foreground galaxy have significantly brightened the X-ray emission from these higher redshift AGNs, allowing their detection. It is suggested that microlensing may be responsible for a significant alteration of the inherent QSO luminosity function.

Stocke, John T.↗

NASA NTRS1987

Radio continuum observations of early- and late-type spiral galaxies

Two complete subsamples of early and late type spiral galaxies were mapped with the VLA in order to explore their radio and optical properties. The choice of the samples is explained, and the observational procedure and data reduction are described. The detection rate was 97 percent, with a detection limit of the order of 1-2 mJy. Total intensity data at 20 cm are presented for the whole sample, and 6 cm data for 11 galaxies. The results are presented in the form of tables and radio contour maps, and are discussed in comparison with previous work.

Gioia, Isabella M.↗

NASA NTRS1987

1E 1048.5 + 5421 - A new 114 minute AM Herculis binary

The discovery of a new AM Herculis binary system, found as a serendipitous Einstein X-ray source, is described. Like the previously discovered mass-transfer binaries involving synchronously rotating magnetic white-dwarf primaries, the system exhibits strong circular polarization, X-ray and optical continuum variations, and optical emission lines, all of which seem to be modulated with these binary periods of 114.5 + or - 0.2 minutes. Although all data are not concurrent, the new system appears to possess the highest ratio of F(x)/F(opt) yet found for an AM Her system. The surprising accumulation of AM Her variables with periods near 114 minute is commented on.

Morris, Simon L.↗

NASA NTRS1987

X-ray surveys as tools to investigate the cosmological evolution of quasars, BL Lac objects and clusters of galaxies

A progress report on a major extension of the Einstein Observatory Medium Sensitivity Survey (MSS) is presented. The MSS consists of X-ray sources serendipitously discovered with the IPC on board the Einstein Observatory in the energy range 0.3-3.5 keV, at fluxes between 10 to the -11th and 10 to the -13th ergs/sq cm/s. The basic properties of the extragalactic sources identified with AGN and clusters of galaxies are discussed.

Gioia, Isabella M.↗

NASA NTRS1987

X-ray selected high redshift clusters of galaxies

Studies of the evolution of X-ray emission from clusters of galaxies have so far used distant clusters discovered optically and then observed at X-ray wavelengths (Henry et al., 1982; Henry and Lavery, 1984). A different approach to the study of cluster evolution is to use clusters selected directly by their X-ray emission, since X-ray selection is extremely successful at discovering high-redshift clusters (up to z = 0.5). The Extension of the Medium Sensitivity Survey, a study of serendipitous X-ray sources discovered with the Einstein Imaging Proportional Counter, has so far provided a sample of more than 60 clusters with relatively high redshifts. Upon completion of the identification programs the sample will include over 100 clusters. Here the data currently available are presented, and the basic properties of this new sample of clusters of galaxies are discussed. A preliminary number-counts distribution is also derived.

Gioia, Isabella M.↗